This invention relates generally to techniques for monitoring a water flow conduit to detect water leakage, and more particularly to a monitoring system in which like flow-meters, each generating a pulse signal whose frequency depends on flow rate, are respectively interposed in the inlet and outlet lines of the conduit to produce output signals which are compared to determine whether a frequency difference exists therebetween indicative of leakage.
Iron ore is reduced to pig iron in a blast furnace. Circumferentially disposed near the top of the hearth section of the furnace are tuyeres which function to admit air therein for combustion, each tuyere being cooled by water passing through a flow conduit. It is important to detect water leakage from the conduit; for should leakage occur, the quality of iron produced by the furnace will be degraded. Moreover, with heavy water leakage, there is danger of explosion. Monitoring of the cooling water is therefore essential.
To carry out such monitoring, it is known to use a pair of vortex-shedding or Karman-type flowmeters, one being interposed in the inlet line to the cooling conduit, and the other in the outlet line therefrom. A vortex flowmeter includes an obstacle in the flow path which generates fluidic oscillations as a function of flow rate, these oscilations being sensed to produce a pulse signal whose frequency is proportional to flow rate. The pulse output signals from the pair of flow-meters are applied to a comparator which yields an analog output signal that depends on the difference in frequency between the applied signals.
Ideally, with flowmeters of identical size and type, no difference signal will be yielded by the comparator in the absence of any leakage, for then the inlet and outlet flow rates will be the same and the resultant output pulse signals from the like flowmeters will be equal. But in practice, no two flowmeters, even though nominally identical, will have exactly the same input-output conversion characteristics. Hence for a given flow rate, each meter will produce an output pulse signal which differs in frequency from the signal produced by the other supposedly-identical meter. Thus flowmeters are subject to so-called instrumental error.
While it has heretofore been known to provide in conjunction with each flowmeter in the monitoring system an adjustable converter to effect span adjustment thereof in order to bring about a proper match of the flowmeter pair, such individual adjustments to correct for instrumental error are difficult to carry out, and are time-consuming, particularly when in a given blast furnace installation, there are more than twenty tuyeres, each with a cooling conduit whose water flow must be monitored.